1. Field of the Invention
The present invention relates to a function expanding method for a display device which displays conditions of an external apparatus that is controlled by a programmable controller. The programmable controller is a so-called programmable logic controller, a PLC, a sequencer, or the like, and it is referred to as a PLC hereinafter.
2. Description of the Related Art
PLCs are used for controlling external apparatuses such as factory equipment. As an HMI (human-machine interface) of a control system, a display device can display conditions of an external apparatus controlled by the PLC and can operate the external apparatus as well. An operation component (HMI component) for operating the external apparatus is displayed on the display device. A user operates the external apparatus through operating the operation component displayed on the display device. An example of such display device is a programmable display device, which is used by being installed at a place where a control board and the like are placed.
The industrial usage of this type of display device has been expanded dramatically, and such display device has been used by being installed at places where there are drastic changes in environmental temperatures and at scenes of cold districts and the like. The display device includes a type which comprises a touch panel for allowing a direct operation of the operation component that is displayed on a display screen, and a type which comprises no touch panel so that the operation component on the display screen cannot be touch-operated with fingers and the like directly. Further, the display device is normally fitted into a display device attachment opening of a control board (not shown) from a front of the display device main body so as to be engaged with an outer periphery of the display device attachment opening to be fixedly mounted to the opening.
While such device is required to comprise various functions in accordance with the expansion of its usage, usage of small-sized and inexpensive display devices has been expanding.
However, when the display device is small, it is difficult to mount various required functions to that single device. Thus, small-sized display devices corresponding to each required function are fabricated in the actual circumstances. Because of that, the manufacturing cost becomes increased. Further, the required functions may change at the scene, so that it is not easy to follow the changes. In such case, it becomes necessary to prepare many types of small-sized display devices, for example, thereby increasing the cost as well as the time and effort further.
Even if various types of slots and connectors are attached to a rear part of the small-sized display device and function expanding modules are mounted to those slots and connectors so as to expand the functions of the small-sized display device, the number of function expanding modules placed thereto is restricted because the area of the rear part is small. Further, when the function expanding modules are placed in other parts than the rear part of the small-sized display device, the advantage of the small-sized device as being small in size, becomes spoiled.
Japanese Unexamined Patent Publication H11-215217 discloses a technique which makes it possible to mount a plurality of types of option apparatuses (function expanding modules) to a casing of a portable information terminal device simultaneously, and makes it possible to operate any of the arbitrary option apparatuses that are mounted to an option apparatus mount mechanism through operations of a touch panel of a display device.
Japanese Unexamined Patent Publication 2003-018678 discloses a technique which makes it possible to select function expanding modules that can collect prescribed monitor data among a plurality of types of function expanding modules which can collect different monitor data from each other except specific monitor data, and makes it possible to connect those selected modules detachably and to be capable of performing data communication with each other.